The present invention relates to a liquid crystal medium for a liquid crystal display and an electro-optical liquid crystal display using the same. More specifically, the present invention relates to an electro-optical liquid crystal display {so-called in-plane switching mode (IPS mode) display in which an electric field for re-aligning a liquid crystal layer works parallel to the liquid crystal layer} having a re-aligning layer for re-aligning a liquid crystal in which an electric field therefor has an effective ingredient parallel to the liquid crystal layer and containing a liquid crystal medium having a positive dielectric anisotropy and to a liquid crystal medium used for the same electro-optical liquid crystal display.
In conventional liquid crystal displays (TN, STN, OMI and AMD-TN), a great part of an electric field working for re-alignment operates vertically to a liquid crystal layer. A liquid crystal display in which an electric field gives electric signals in such a mode that the electric field has an effective structural element parallel to a liquid crystal layer is described in International Patent Application WO 91/10936 [in-plane switching (IPS)]. Such operation principle of a display is described in, for example, A. Soref, Journal of Applied Physics, Vol. 45, No. 12, p.5466 to 5468 (1974). Possibility of various addresses in such a display is disclosed in EP 0588 568.
These IPS displays can be operated by using a liquid crystal material having either positive or negative dielectric anisotropy (xcex94xcex5xe2x89xa00). However, use of conventionally known materials allows the IPS displays to cause a image sticking and result in having a relatively high threshold voltage and a long response time. Accordingly, there has been present in the IPS displays, a subject to clarify liquid crystal materials which do not cause burning and are suitable for achieving a relatively low threshold voltage and a short response time. It is described in, for example, Japanese Patent Application Laid-Open No. 125063/1997 that used is a liquid crystal medium characterized by containing at least one compound containing a 4-cyclohexylcarbonyloxy) benzonitrile group which is laterally substituted with fluorine, whereby the rotational viscosity coefficient (xcex31) has been reduced to 80 to 120 mPa. second. However, it has never been described therein to inhibit burning from being produced.
As apparent from the descriptions given above, an object of the present invention is to provide a liquid crystal medium which is suitable for an IPS mode causing no burning and achieving a relatively low threshold voltage and a considerably short response time and an electro-optical liquid crystal display of the IPS mode comprising the same.
The liquid crystal composition of the present invention comprises the following structures:
(1) A liquid crystal medium used for an in-plane switching mode (a so-called IPS mode in which an electric field for re-aligning a liquid crystal layer works parallel to the liquid crystal layer) display, comprising 5 to 37.5% by weight of at least one compound as a first component selected from the group consisting of compounds represented by Formula (I), 5 to 62.5% by weight of at least one compound as a second component selected from the group consisting of compounds represented by Formula (II) and the balance of another liquid crystal compound containing crystal medium having a positive dielectric anisotropy, wherein the first component is a compound represented by Formula (I): 
(wherein R1 represents an alkyl group, an alkoxy group or an oxalkyl group (containing 1 to 4 oxygen atoms) having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms; X represents transcyclohexylene or phenylene; A represents xe2x80x94COxe2x80x94Oxe2x80x94 or a single bond; and Y1 represents a hydrogen atom or a fluorine atom), and the second component is a compound represented by Formula (II) 
(wherein R2 represents an alkyl group, an alkoxy group or an oxalkyl group (containing 1 to 4 oxygen atoms) having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms).
(2) A liquid crystal medium used for an in-plane switching mode (IPS mode) display, comprising 5 to 37.5% by weight of at least one compound as a first component selected from the group consisting of compounds represented by Formula (I), 5 to 62.5% by weight of at least one compound as a second component selected from the group consisting of compounds represented by Formula (II), 5 to 37.5% by weight of at least one compound as a third component selected from the group consisting of compounds represented by Formula (III) and the balance of another liquid crystal compound containing a liquid crystal medium having a positive dielectric anisotropy, wherein the first component is a compound represented by Formula (I): 
(wherein R1 represents an alkyl group, an alkoxy group or an oxalkyl group (containing 1 to 4 oxygen atoms) having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms; X represents transcyclohexylene or phenylene; A represents xe2x80x94COxe2x80x94Oxe2x80x94 or a single bond; and Y1 represents a hydrogen atom or a fluorine atom); the second component is a compound represented by Formula (II): 
(wherein R2 represents an alkyl group, an alkoxy group or an oxalkyl group (containing 1 to 4 oxygen atoms) having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms); and the third component is a compound represented by Formula (III): 
(wherein n is 0 or 2, and R3 represents an alkyl group, an alkoxy group or an oxalkyl group (containing 1 to 4 oxygen atoms) having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms).
(3) The liquid crystal medium for an IPS mode display as described in the above item (1), comprising the compound represented by Formula (I) in which X is phenylene, and A is xe2x80x94COxe2x80x94Oxe2x80x94.
(4) The liquid crystal medium for an IPS mode display as described in the above item (2), comprising the compound represented by Formula (I) in which X is phenylene, and A is xe2x80x94COxe2x80x94Oxe2x80x94.
(5) The liquid crystal medium for an IPS mode display as described in the above item (2), comprising the compound represented by Formula (I) in which R1 is a linear alkenylgroup having 2 to 10 carbon atoms and X is phenylene and in which A is xe2x80x94COxe2x80x94Oxe2x80x94; the compound represented by Formula (II) in which R2 is a linear alkyl group having 1 to 10 carbon atoms or a linear alkenyl group having 2 to 10 carbon atoms; and the compound represented by Formula (III) in which R3 is a linear alkyl group having 1 to 10 carbon atoms or a linear alkenyl group having 2 to 10 carbon atoms.
(6) The liquid crystal medium for an IPS mode display as described in any one of the above items (1) to (5), wherein the volttage holding ratio is controlled to 40 to 90%.
(7) An active matrix type liquid crystal display element for an IPS mode display, characterized by comprising the liquid crystal medium as described in any one of the above items (1) to (6), wherein a product of a optical anisotropy (xcex94n) and a cell thickness (d) of the liquid crystal medium has a value falling in a range of 200 to 350 nm.
(8) An IPS mode display provided with the liquid crystal display element as described in the above item (7).